Homologous Compounds ZnnIn2O3+n (n = 4, 5, and 7) Containing Laminated Functional Groups as Efficient Photocatalysts for Hydrogen Production.

Strong visible light absorption and high charge mobility are desirable properties for an efficient photocatalyst, yet they are hard to be realized simultaneously in a single semiconductor compound. In this work, we demonstrate that these properties coexist in homologous compounds ZnnIn2O3+n (n = 4, 5, and 7) with a peculiar layered structure that combines optical active segment and electrical conductive segment together. Their enhanced visible light absorption originates from tetrahedrally or trigonal-bipyramidally coordinated In atoms in Zn(In)O4(5) layers which enable p-d hybridization between In 4d and O 2p orbitals so that valence band minimum (VBM) is uplifted with a reduced band gap. Theoretical calculations reveal their anisotropic features in charge transport and functionality of different constituent segments, i.e., Zn(In)O4(5) layers and InO6 layers as being for charge generation and charge collection, respectively. Efficient photocatalytic hydrogen evolution was observed in these compounds under full range (λ ≥ 250 nm) and visible light irradiation (λ ≥ 420 nm). High apparent quantum efficiency ∼2.79% was achieved for Zn4In2O7 under full range irradiation, which is almost 5-fold higher than their parent oxides ZnO and In2O3. Such superior photocatalytic activities of these homologous compounds can be understood as layer-by-layer packing of charge generation/collection functional groups that ensures efficient photocatalytic reactions.